Debt Collectors: Medical Debt Collection No Bill Received

I went to the dermatologist last August, provided my insurance card, has services rendered, no payment was requested. That December I started receiving calls from the doctors office. I called them numerous times, left numerous messages asking them to call my cell, not home as I'm at work during the day..They were impossible to get a hold of. Finally in February I spoke to someone who wanted to confirm my address. They had the wrong address on file, not even close to my address and I have no clue where it came from. I corrected it. Later in February I went back for a follow up visit. At this visit nor at any time prior to this visit was I informed I owed anything. Additionally at this point they had my correct address on file. I just received a call from a collection company this morning stating I owed the doctors office from my visit in August???? I have NEVER received a bill due to their incorrect information in the system. They never informed me of this over the phone when I spoke to them or when I was there in person. I have never been sent to collection before for any reason. How do I resolve this. I went to the office and they said it was out of their hands and asked me to leave?!?!? I have no problem paying this but I do not want to pay a collection agencey and have this on my credit when this was never my issue to begin with.

Debt Collectors: Medical Debt Collection, No Bill Received